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Engine and Gearbox mounting plates for C'do engine in F'bed

Discussion in 'Norton Commando Motorcycles (Classic)' started by laurentdom, Dec 19, 2012.

  1. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Laurentdom
    I remade the engine plates for my Norton 500 single in a slimline frame because I wanted to use Commando primary cases which move the gearbox closer to the engine.
    I will list the steps I went through in case any of it is useful to you.
    • Went through 2 or 3 iterations of making them from 1/4" Craftwood before I was happy with layout. (edit - I started by tracing the outline of the original plates onto the Craftwood and worked forward from there)

    27 Oct '10 2.JPG
    BTW - the flat-top extensions on the lower-rear plates are where I mount my battery​
    31 Oct '10 9.jpg
    • Next traced the outline, including bolt-holes, onto pieces of A3 (edit) paper
    • Then scanned these into PDF format
    • A draftsman mate the used one of his programs to convert them to AutoCad. He also ensured the boltholes were round and undersize (more on that below) and smoothed the outline.
      • Ken McIntosh (NZ) advised me to make the holes undersize and ream to suit to unsure a stiffer and more durable final product. I think he's right on the money there.
    • I took these Autocad drawings to a local sheetmetal works where they used the program in their water-jet cutter on a piece of 8mm aluminium alloy plate.
    • Then, using gradually fine grades of abrasive cloth/paper I smoothed the outside.
    • Next I reamed the top rear holes to suit the removable frame crossbar.
    • Now, having both plates bolted to the crossbar I reamed the holed for the crankcases.
    • Next, with the plates bolted to both the crossbar and the crankcases I:
      • reamed the mounting holes for the gearbox and,
      • fitted the plates/crankcase assy into the frame and reamed the lower rear holes and the centre-stand/mount holes.
    • Lastly I reamed the small front plates to suit both the crankcases and frame. (the slimline for singles has 2 bolts for the frame and 2 bolts for the engine - different to the frame for twins)
    • Mounted the bolts (all satin chromed - most from McIntosh racing) using ACF-50 to prevent corrosion
    9 Jan '11 4.JPG 9 Jan '11 7.JPG

    Let me know if you want any more information
    Cheers
    Rob
     
    Last edited: Mar 14, 2019
    gortnipper likes this.
  2. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    I'll try to attach the pdf files of the rear plates here - PM me with your email address if you want the AutoCad files ( not for your engine though remember)
     

    Attached Files:

  3. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Laurentdom
    Another point to be careful of if you buy old plates to suit 650ss is to check the front/bottom bolt holes of the rear plates. Many have been butchered from a hole into a bottom-opening slot - I presume to make fitment easier. Will definitely compromise the stiffness and durability of the final assembly.
    Some unscrupulous ebay sellers deliberately omit this detail from their photos.
    Cheers
    Rob
     
    Last edited: Mar 14, 2019
  4. ashman

    ashman

    Joined:
    Jul 11, 2010
    Rob this thread started back in 2012 when Laurenton asked about these plates and he hasn't been back on this thread since so old threat reappearing same as my pic of my plates was back in 2016.

    Ashley
     
  5. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Ta Ashley - I should be more careful.
    Recent question was by Piero so I'll answer him
    Cheers
     
  6. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Piero
    I mistakenly replied to Laurentdom instead of you with my 3 posts above - may be of interest to you?
    Cheers
    Rob
     
    Last edited: Mar 14, 2019
  7. ashman

    ashman

    Joined:
    Jul 11, 2010
    All good Rob I just got new reading eyes and starting to pick up little things like that lol, hoping to get up your way soon, be good to get together for a few beers.

    Ashley
     
  8. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Too right - I'll have to practice some more!!
     
  9. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Thank you.
    Piero
     
  10. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    I have used steel engine plates in a featherbed, but they were too heavy. I usually use 8mm aluminium, but I always make the plates FULL CIRCLE. I join the bits behind the gearbox from top to bottom. When the engine vibrates in the frame - with the open type plates, the corner at the top in front of the gearbox becomes a stress raiser, where cracking often occurs. You can also get cracking of the frame tubes where the rear swing arm gussets end. With full circle engine plates, depending on which gearbox you use, sometimes you have to fit the right hand plate to the gearbox before putting the assembly into the frame. It can be tricky, but overall it makes for a better result.

    https://ibb.co/FV1tx61
     
    Last edited: Mar 15, 2019
  11. ashman

    ashman

    Joined:
    Jul 11, 2010
    If your motor is balanced right they get no vibrations through the engine plates and after 37 year or more now I have proven this with no cracks at all the most important thing is the have a very strong head steady, witout that it will crack the down tubes, I was going to work on a friends mate bike once and he was running with out a head steady for some time and his frame was just about to crack right through, he was told by someone it wasn't needed till I showed him the cracks, I wouldn't work on the bike till he got it fixed, never did see him again, some poeple just can't be told, my friend was upset with me because I stuck it into his mate about it, I said to my mate why send me someone who think they knows better lol.
    So now I don't do any jobs for friends of friends who I don't know not worth the hassles.

    Ashley
     
  12. robs ss

    robs ss VIP MEMBER

    Joined:
    Aug 16, 2016
    Very true Ash.
    The weak point of featherbeds (both types) is the crossover between the downtubes and the horizontal ones under the tank.
    The main task for a featherbed head-steady is not to steady the head but to use the head to brace the top of the steering headstock.

    Rob
     
  13. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    My friend with the Triton, removed the turnbuckle on his Manx frame and welded in a tube from the steering heard to the first cross tube. It stops the trail from changing. With a Manx, as you tighten the turnbuckle, you change the handling.
     
  14. ashman

    ashman

    Joined:
    Jul 11, 2010
    I find my 5mm steel engine plates are not that much differents to using thicker alloy engine plates in weight wise but when I did make alloy engine plates I had more vibrations but I only had 6mm alloy at the time and I ended up going back to my steel plates, if I used 8mm alloy plates might have been different but the weight savings would have been sweat FA and the steel plates had very little vibrations at all, so I stuck with the steel plates.
    I also run a long through bolt from the middle of the bottom frame rail with spacers right through the engine mounts to the other side of the frame, this stiffens everything up nice and tight which stop all vibrations.

    Ashley
     
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